This invention relates to the recovery of antimony from antimony-containing materials, particularly ores, ore concentrates, smelter flue dusts, metals or the like. This invention also relates to the safe treatment of such materials which contain antimony and arsenic.
Several types of ore and similar materials contain significant amounts of antimony and arsenic. In refining metals from the various ores, it is desirable to separate the antimony and arsenic from the target metals. Many antimony products are also marketable, so it is desirable to recover these antimony compounds in as pure a form as commercially reasonable. Additionally, arsenic-containing products and waste products resulting from these separation processes must be treated with care to minimize pollution control problems. In that regard, it is often desirable to separate arsenic and arsenic-containing compounds from these materials in stable forms that may be conveniently, economically, and safely disposed.
Certain prior art methods have been proposed and used for separating antimony and arsenic from materials such as ores and ore concentrates. The most prevalent prior art method involves a pyrometallurgical process known as liquation in which ores containing antimony in the form of stibnite are heated to above the melting point of stibnite. This temperature is very low relative to the melting points of the other metal sulfides which are contained in the ore. The stibnite melts and "drains" preferentially from the rest of the ore and can then be collected. Similarly, antimony oxide production by oxidative roasting is common. These prior art processes suffer greatly from their inability to effectively separate impurities from the final antimony products.
In addition, certain prior art hydrometallurgical processes have been proposed or developed to avoid pollution control problems arising from the use of such smelting processes. Nonetheless, such prior art hydrometallurgical processes suffer from various shortcomings, particularly with respect to the leaching of the ore or other material and with respect to the purity of the antimony products obtained. For example, in leaching stages of these prior art processes, undesirably high percentages of antimony can be left in the insoluble leach residue. Also, expensive solvents or reagents are used which are not easily regenerated or recycled.
Antimony is often present in the material to be treated in both its +3 (trivalent) and +5 (pentavalent) valence states. It is desirable during leaching to obtain an antimony product in its +5 state rather than its +3 state (i.e., as sodium thioantimonate rather than sodium thioantimonite). This is because the crystallization qualities of antimony in its +5 valence state are greatly enhanced compared to the crystallization qualities of antimony in its +3 state.
Some solvents may perform acceptably when used in connection with ores containing antimony in its pentavalent form but perform inadequately when antimony is present in its trivalent form. Additionally, prior art processes for treating materials including antimony in its trivalent form often require two stage leaching. This adds to the cost and complexity of the processes and disadvantageously results in a diminished percentage recovery of antimony. Also, antimony products produced using such prior art processes are of relatively low purity, and the contained impurities impair the commercial value of the antimony products.
Finally, it has been discovered that smelter flue dust often contains excessive amounts of arsenic and antimony making the flue dust a hazardous waste. As such, disposal of the flue dust must be handled with great care and at great expense. Such flue dusts also may contain valuable constituents such as Cu, Cd, Ga, Te, Sn, Ge, Zn, Pb, In, Ag, Au, and platinum group metals.